1. Field of the Invention
The present invention relates to a package for a semiconductor chip and a method of forming the same. More particularly, the invention relates to a multi-row semiconductor package with an improved leadframe and a method for making said package.
2. Description of the Related Art
Semiconductor devices and integrated circuits (ICs) are made up of components, such as transistors and diodes, and elements such as resistors and capacitors, linked together by conductive connections to form one or more functional circuits. Interconnects on an IC chip serve the same function as the wiring in conventional circuits.
Once the components of an IC package have been assembled, the package is typically sealed by plastic encapsulation in order to improve the strength of the package and to provide necessary protection to the components within.
One type of package is a single sided multi row quad flat no-lead (QFN) package. See for example FIGS. 1 and 2. A multi row QFN is a type of copper leadframe based semiconductor package with more than one row of terminals at the bottom surface of the package to at least one peripheral side for the purpose of providing interconnection to external devices for example PCB.
Single sided multi row QFN packages can be singulated by two main methods, punch singulation and sawn singulation. However, both methods have several problems associated with them. For example, with punch singulation, solder bridging 101 can occur during solder plating and lead-to-lead shorting 102 can occur during package singulation. See FIGS. 1a and 1b respectively, which are top views of a portion of FIG. 1. FIG. 1b corresponds to the rectangular box drawn on top of FIG. 1. Solder bridging is a defect where solder bridged between adjacent leads. Lead-to-lead shorting is an un-wanted connection between neighboring leads caused by the inherent solder squeeze-out during package singulation. The existence of such defects in the package will affect the quality and functionality of the device.
Likewise, a single sided multi row QFN package, such as that shown in FIG. 2, formed by being sawn singulated, also has several problems associated with it. For example, adjacent leads 201 and 202 can be shorted as a result of the inherent smearing 203 of the copper material during package singulation. See FIG. 2a, which is a side view of a portion of FIG. 2 indicated by the circle in FIG. 2.
One object of the present invention is to produce a single sided multi-row package that reduces or eliminates solder bridging and lead-to-lead shorting when the package is punch singulated.
Another object of the present invention is to produce a single sided multi-row package that reduces or eliminates shorting of adjacent leads caused by smearing when the package is sawn singulated.
The invention can also act as an interlock that reduces the risk of having a separation between the mold cap and the leadframe. It also improves reliability by preventing the moisture to easily penetrate through the interface between the outer leads and mold cap.